The present invention relates to a scrolling color projector, and more specifically to the phase control for a colored light scanner of a scrolling color projector.
A scrolling color projector produces full color images from a single light modulator by illuminating a liquid crystal panel with multiple stripes of colored light (red, green, blue) that continuously scroll, from top to bottom, over the liquid crystal panel. In order to scroll the multiple stripes of colored light over the liquid crystal panel, the strolling color projector includes a scanner for each color of light to be scrolled over the liquid crystal panel. Each scanner includes a prism connected to the shaft of a motor. The motor controls rotation of the prism. Also attached to the motor is a precision optical encoder which provides information regarding the position of the motor shaft, and correspondingly the rotation of the prism and the scan of each stripe of colored light on the panel.
The precision optical encoder provides information for control of the motor and correspondingly for control of the prism. The phase and rotation of the prism are important because each stripe of colored light must be projected and scrolled on the liquid crystal panel at specific times in relation to video information that is provided to the liquid crystal panel. That is, the red, green and blue stripes of light must be present on a line of the panel concurrent with the presentation of the corresponding video information for that particular line. The optical encoder serves to synchronize the phase of rotation of the prism (the scan of the color stripes) with the presentation of the video information. As a result, each stripe of light, as it is being scrolled down the liquid crystal panel, appears on a particular display line coincident with the corresponding video information for that color of light.
A drawback to the prior art device is that the precision optical encoder is very costly. Typically the optical encoder costs more than the entire scanner, i.e., more than the cost of the prism and the motor together. It would therefore be beneficial to provide synchronization of scan of each color of light over the liquid crystal panel with the video information without the use of an external precision optical encoder.
It is an object of the present invention to provide a method and apparatus which provides phase control for a colored light scanner of a scrolling color projector which does not use an optical encoder.
It is a further object of the present invention to provide a method and apparatus which provides phase control for a colored light scanner of a scrolling color projector which is less expensive than prior art phase controls for colored light scanners.
It is yet another object of the present invention to provide a method and apparatus which provides phase control for a colored light scanner of a scrolling color projector and which utilizes the back EMF of a motor coupled to a prism of the scanner to synchronize the phase of the colored light scanner with the presentation of video information on the panel.
It is still a further object of the present invention to overcome inherent disadvantages of known phase control systems for a colored light scanner for scrolling color projectors.
In accordance with one form of the present invention, a scanner phase control for a scrolling color projector includes a light source for generating an input light, a color splitter operatively coupled to the light source for at least one of transmitting and reflecting the input light emitted from the light source to extract at least a first color light, and a first color scanner operatively coupled to the color splitter. The first color scanner including a motor and a prism and receiving as an input the first color light. The motor rotating the prism to scan the first color light. The scrolling color projector also includes a reference phase generator for generating a reference phase signal indicative of timing information for scanning the first color light including when a scan of the first color light should begin, a motor back-EMF sensor coupled to the motor and generating a motor back-EMF signal indicative of the back-EMF of the motor wherein the prism is coupled to the motor such that a motor back-EMF signal zero crossing is indicative of a beginning of a scan for the first color light. The scrolling color projector further includes a phase detector coupled to the reference phase generator and the motor back-EMF sensor. The phase detector receiving the reference phase signal and the motor back-EMF signal and generating a signal such that the motor back-EMF signal zero crossing is coincident with the beginning of a scan of the first color light as indicated by the reference phase signal.
In accordance with another form of the present invention, a scanner phase control for scrolling a color projector includes a light source for generating an input light, a color splitter operatively coupled to the light source for at least one of transmitting and reflecting the input light emitted from said light source to extract first, second and third color lights, and a first color scanner operatively coupled to the color splitter and including a motor and a prism. The first color light scanner receiving as an input the first color of the input light and providing a first color light output signal. The motor rotating the prism to scan the first color light output signal. The scanner phase control also includes a second color scanner operatively coupled to the color splitter and including a motor and a prism. The second color scanner receiving as an input the second color light of the input light and providing a second color light output signal. The motor of the second color scanner rotating the prism of the second color scanner to scan the second color light output signal. The scanner phase control also includes a third color scanner operatively coupled to the color splitter and including a motor and a prism. The third color scanner receiving as an input the third color light of the input light and providing a third color light output signal. The motor of the third color scanner rotating the prism of the third color scanner to scan the third color light output signal. The scanner phase control further includes a color recombiner for receiving as an input the first, second and third scanner output signals and providing a recombined light signal, a polarizing beam splitter for at least one of transmitting and reflecting the recombined light signal according to a polarization component thereof, and a phase detector operatively coupled to each of the motors. The phase detector receiving as a first input a signal indicative of the phase of rotation of each of the motors of the first, second and third color scanners, and as a second input a reference phase signal indicative of timing information for scanning each of the first, second and third color lights. The phase detector generating a signal such that each of the motors of the first, second and third color scanners is rotated in accordance with the reference phase signal.
In accordance with another form of the present invention, a scanner phase control coordinates a phase of scanning of a stripe of light provided by a prism of a color light scanner, with a video signal provided to a display. The prism being coupled to a motor such that the start of a scan coincides with a motor back-EMF value of zero. The scanner phase control including a phase detector operatively coupled to the motor. The phase detector receiving as a first input a signal indicative of the back-EMF zero-crossings of the motor. The phase detector also receiving as a second input a reference phase signal indicative of timing information for scanning the stripes of light, wherein when the reference phase signal indicates the beginning of a scan of the stripe of light, the phase of the motor is altered such that the value of the motor back-EMF is zero.
Another form of the present invention is directed to providing method of providing scanner phase control for a scrolling color projector. The scanner phase control coordinates a phase of scanning of a stripe of light provided by a prism of a scanner with a video signal. The prism being coupled to the motor such that the start of a scan of a stripe of light provided by the prism coincides with a motor back-EMF value of zero. The method including the steps of monitoring the motor back-EMF value, providing a reference phase signal corresponding to timing information for the scan of the stripes of light, determining a beginning of a scan from the reference phase signal, and altering the phase of the motor such that the motor back-EMF zero value coincides with a beginning of a scan as identified by the reference phase signal.
A preferred form of the scanner phase control for a scrolling color projector and method of providing scanner phase control as well other embodiments, objects, features and advantages of the present invention will become apparent from the following detailed description of illustrative embodiments, which is to be read in connection with the accompanying drawings.